1. Field of the Invention
The present invention relates to a device for controlling the idling operation of an internal combustion engine which is adapted to control the number of engine revolution per unit time (hereinafter referred to as RPM) during idling to a desired value by changing the opening area of an intake passage in accordance with the temperature of engine cooling water.
2. Description of the Prior Art
In general, a device for controlling the idling operation of an internal combustion engine by changing the opening area of an intake passage has been known which employs an acutator for changing the closed-side stop position of a throttle valve disposed in the intake passage to control the RPM of the engine during idling to a desired value. In this type of idling operation cntrolling device, the RPMs of the engine is sensed by a RPM sensor and input to a control unit which compares the actual RPMs thus sensed with a preset object value so that the engine is controlled in a feedback manner to make the RPMs converge into the object value. Also, an actuator position sensor is provided to sense the position of the actuator and the actuator position thus sensed is input to the control unit so as to control the actuator position to a preset objected position so that the opening degree of the throttle valve, which is operated by the actuator, is controlled in a feedback manner. Further, in order to perform the fast-idling operation of the engine, the objected position of the actuator is preset in a manner such that the actuator position and hence the throttle valve poition comes to a relatively large opening degree when the temperature of the engine cooling water is low as illustrated by a solid line curve A in FIG. 5.
In the above-described idling operation controlling device, there is no problem when the control unit for controlling the actuator in the above manner operates normally without any failure, but if the control unit has failed so that an abnormal signal is output to the actuator to cause it to open excessively from the preset objected position in spite of the fact that the temperature of the engine cooling water becomes high after the warming-up operation of the engine has been completed, the RPMs of the enigne during idling is abnormally increased to a dangerous level.